Nearly two-thirds of the Escherichia coli chromosome contains regions of unknown genetic importance. Gene organization in E. coli is similar to that of Salmonella typhimurium, and regulation of gene expression is comparable in both. The homology of gene organization between diverging species implies a high degree of organizational conservation. Genes for related metabolic functions are frequently clustered and evolution of gene controls may have facilitated gene grouping. In other cases genes for physiologically related functions are dispersed on the chromosomes in conserved order. Although the relationship of chromosome organization to evolution of genes and gene controls is not understood, the dispersion of related genes may have resulted from non-tandem duplication of existing genes and subsequent mutational drift. This is a continuation study of mechanisms that control genes functionally related, but genetically dispersed in bacteria. Acetohydroxy acid synthase isozymes in E. coli K-12 are encoded by 2 active (ilvI, ilvB) and 4 silent (ilvG, ilvJ, ilvF, ilvK) gene regions which are dispersed. The silent genes can be mutationally activated, and this study will focus on their function, relatedness, control, and possible role(s) in chromosome evolution. Standard biochemical and recombinant DNA technologies will be utilized to clone and restriction map gene regions in active and inactive states; probe the w.t. chromosomes of E. coli and S. typhimurium for homologous regions; compare sequences of active and silent alleles to determine structural relatedness to all ilv genes, and mechanisms of activation; analyze base sequences for consensus control sequences; measure promoter efficiencies; study gene expression in maxicells to look for silent gene function; examine the physiological controls of each gene region; and measure effects of active and silent alleles on strain fitness.